It is proposed to study the immune responses in the Patas monkey (Erythrocebus patus) during experimental infection with Brugia malayi. To measure antibody responses to developmental stages of the parasite and to characterize the peripheral cellular responses by in vitro lymphocyte activation with parasite antigens and mitogen. Cellular and humoral immune responses to isolated fractions of the parasite stages and their products will also be examined and correlated with infection protocol, microfilaremia and any obvious lymphatic pathology. Comparison will be made of the antibody responses in the Patas monkey, which develops chronic, patent infections and the Rhesus monkey which often develops cryptic infections to determine if these differences in host-parasite relationship can be correlated with differences in immune responses. The objective of the study is to obtain information on the immunologic responses to a lymphatic dwelling filaria in an experimental model which may closely parallel the responses of man and thus contribute to understanding the immunobiology of human filariasis.